How much current can a 12V 5Ah SLA battery supply?

[PNjunction]

If I were to put this into a solar charger I would be using something like a 50 to 100 watt panel. The battery is not made to be slow charged.

Funny you should mention that - I'm now running 100 watts of panel through a Morningstar charge controller into a 12v, 5ah agm - but it is a homebrew 6-pack of Enersys-Hawker Cyclon agm batteries, (two 6v monoblocs in series) where the cost of admission is a minimum current input of C * 0.4

This will have to do until Trojan makes a 5ah battery.

[PNjunction]

To make a long story short, I bought it, used it to charge a phone at 280mA over 5 hours, then charged a few other things, then set it up outside with a solar panel project that failed (That's another story) but I think it became deeply discharged. I am not entirely sure but the standing voltage was at 11.7V.

Remember that for most cycling purposes, you don't want to take the battery below 50% capacity for the longest cycle life. Ideally one would want to fall no less than say 20-25%. So in reality, if you want more than a handful of cycles out of it, you only have 2.5ah (50%) to play with.

You can get a rough idea by measuring the SOC voltage after a 4 hour rest of no-charge / no discharge:

12.8+ 100% charged
12.5 75% charged
12.2 50% charged
11.95 25% charged
11.95- don't go this low.

Anyway, I put it on a charger yesterday and set the charger to 1.5A because that is what I read on the battery as the "Cyclic Usage" "Initial Current". I later read elsewhere that SLAs are limited to 10% of their amp hours. That would be 500mA. Did I make a mistake? The charger only supplied 1.4 amps to it for about 90 minutes, after which the current slowly decreased. A couple of hours later, it got down to 100mA then the charger shut off.

Sounds normal. Mostly you'll read that these ups style agms can only handle about C/4 max input current. So the limit here of 1.25a makes sense. (5/4). Off hand, this rate is also about the maximum you want to discharge at - otherwise the voltage will crash very fast usually well below the voltage your gear can operate at. But you CAN dump a lot of current fast if you really want to - but look at the Discharge Charecteristic charts (link below) and look how fast pulling 10amps out of that thing will last - about 8 minutes, and thats at 8 volts! Not nice. At the other side of the chart is your cellphone at .25ah. That can go a LOT longer, like 20 hours. (real world usually less)

BUT, charts like these usually show times when totally discharging the battery. You don't want to go there. Cut the times listed in half for duration.

This similar battery specification may help. Look for the Powersonic PS-1250 in the chart and download the pdf documentation.

http://www.power-sonic.com/ps_psg_series.php

Update: that battery is a UPGI UB1250 - the pdf docs for the model D5741 can be found here:

http://upgi.com/products/batterysearch.aspx

Without any test gear, what I might do for a quickie test is just use that cellphone charger if it truly does draw 280 ma for about 9 hours from a fully charged agm. You may have to use the phone a few times to recharge for 9 hours total. 280 * 9 = 2.520a, about 50% of that agm. Let it rest for 4 hours and measure the voltage. If you are nowhere near 12.2 volts, then either the battery is bad to begin with, or you didn't start out with a fully charged agm. Or the load isn't really 280ma constant.

Obviously none of this may be accurate without quality measurements, but I think you get the idea.

[Sunking]

No it is a UPS and Robotic AGM battery. You can charge it at 20 amps if you monitor temperature and voltage. Being a UPS and Robotic battery also means you can discharge it at very high rates up to 4C or 20 amps. If you put it on a 1.5 amp charger for 5 hours and the resting voltage is 11.7 volts, toss it in the trash. FWIW this is not the right type of battery for cycling operations. It is made to discharge at very high rates and only has a few hundred cycle in it, as opposed to thousands of cycles.

If I were to put this into a solar charger I would be using something like a 50 to 100 watt panel. The battery is not made to be slow charged.

[Simon99]

I am trying to diagnose whether I have damaged my new battery by discharging it. Here is a photo of the battery with the specifications and a photo of the current while discharging it.P1110362.JPGP1110365.JPG

To make a long story short, I bought it, used it to charge a phone at 280mA over 5 hours, then charged a few other things, then set it up outside with a solar panel project that failed (That's another story) but I think it became deeply discharged. I am not entirely sure but the standing voltage was at 11.7V.

Anyway, I put it on a charger yesterday and set the charger to 1.5A because that is what I read on the battery as the "Cyclic Usage" "Initial Current". I later read elsewhere that SLAs are limited to 10% of their amp hours. That would be 500mA. Did I make a mistake? The charger only supplied 1.4 amps to it for about 90 minutes, after which the current slowly decreased. A couple of hours later, it got down to 100mA then the charger shut off.

Now I am testing it for discharge. I set the unit at 1A but it will only supply 400mA discharging. Later it went up to 500mA but now it is back at 410mA.

What it the max. current the battery should supply? How can I tell if it is damaged? What should the max charge rate be?